V4.2 is the latest version, and is the version you should be installing.

Can you tell us how you have your runtimes set up? Do you have multiple runtimes? External or default? What is the full path of the runtime you're trying to install V4 in?

Using the DAZ install manager might be easier, if you're not familiar with how to install things in Poser.

Also, make sure you have only one copy of V4 installed. If there's multiple versions (from multiple attempts to install), it won't work.